Described herein are discrete, electrically-interconnected large area photovoltaic cells and adjacent, electrically-interconnected, large area photovoltaic cells. Also discussed as a principal feature of the present invention is the fabrication of a large area photovoltaic cell from a plurality of electrically-isolated, small area segments which must be electrically-interconnected to provide an electrically-operable large area solar cell. Another principal feature of the present invention is the fabrication of a plurality of adjacent, electrically-interconnected, large area solar cells from a plurality of discrete large area photovoltaic cells.
Although crystal silicon devices are the basis of the huge semiconductor industry, devices made from crystal silicon have fixed parameters which are not variable as desired, require large amounts of material, are only producible in relatively small areas and are expensive and time consuming to produce. Devices based upon amorphous silicon can eliminate these crystal silicon disadvantages. Amorphous silicon has an optical absorption edge having properties similar to a direct gap semiconductor and only a material thickness of one micron or less is necessary to absorb the same amount of sunlight as the 50 micron thick crystalline silicon. Further, amorphous silicon can be made faster and more easily in larger areas than can crystalline silicon.
Accordingly, a considerable effort has been made to develop processes for readily depositing amorphous semiconductor alloys or films, each of which can encompass relatively large areas, if desired, limited only by the size of the deposition equipment, and which could be readily doped to form p-type and n-type materials when p-n junction devices are to be made therefrom equivalent to those produced by their crystalline counterparts.
Greatly improved amorphous silicon alloys having significantly reduced concentrations of localized states in the energy gaps thereof and high quality electronic properties have been prepared by glow discharge decomposition as fully described in U.S. Pat. No. 4,226,898, Amorphous Semiconductors Equivalent to Crystalline Semiconductors, issued in the names of Stanford R. Ovshinsky and Arun Madan on Oct. 7, 1980, and by vapor deposition as fully described in U.S. Pat. No. 4,217,374, issued in the names of Stanford R. Ovshinsky and Masatsugu Izu on Aug. 12, 1980, under the same title. As disclosed in these patents, which are incorporated herein by reference, fluorine is introduced into the amorphous silicon semiconductor to substantially reduce the density of localized states therein. It is believed that the activated fluorine readily diffuses into and bonds to the amorphous silicon in the amorphous body to substantially decrease the density of localized defect states therein, because the small size of the fluorine atoms enables them to be readily introduced into the amorphous body. The fluorine bonds to the dangling bonds of the silicon and forms what is believed to be a partially ionic stable bond with flexible bonding angles, which results in a more stable and more efficient compensation or alteration than is formed by hydrogen and other compensating or altering agents. Fluorine is considered to be a more efficient compensating or altering element than hydrogen when employed alone or with hydrogen because of its exceedingly small size, high reactivity, specificity in chemical bonding, and highest electronegativity.
It is now known that the efficiency of a photovoltaic device may be enhanced by stacking cells atop of each other. This concept of utilizing multiple cells, to enhance photovoltaic device efficiency, was discussed at least as early as 1955 by E. D. Jackson in U.S. Pat. No. 2,949,498, which issued on Aug. 16, 1960. The multiple cell structures therein discussed utilized p-n junction crystalline semiconductor devices. Essentially, the concept is directed to utilizing different band gap devices to more efficiently collect various portions of the solar spectrum and to increase open circuit voltage (Voc.). The tandem cell device has two or more cells with the light directed serially through each cell, with a large band gap material followed by a smaller band gap material to absorb the light passed through the first cell or layer. By substantially matching the generated currents from each cell, the overall open circuit voltage of each cell may be added, thereby producing a device which makes full use of the energy produced by incoming light.
It is of obvious commercial importance to be able to mass produce photovoltaic devices. Unlike crystalline silicon which is limited to batch processing for the manufacture of solar cells, amorphous silicon alloys can be deposited in multiple layers over relatively large area substrates to form solar cells in a high volume, continuous processing system. Continuous processing systems of this kind are disclosed, for example, in pending patent applications: Ser. No. 151,301, filed May 19, 1980, for A Method of Making P-Doped Silicon Films and Devices Made Therefrom, now U.S. Pat. No. 4,400,409; Ser. No. 244,386, filed March 16, 1981 for Continuous Systems for Depositing Amorphous Semiconductor Material; Ser. No. 240,493, filed Mar. 16, 1981 for Continuous Amorphous Solar Cell Production System; Ser. No. 306,146, filed Sept. 28, 1981 for Multiple Chamber Deposition and Isolation System and Method; and Ser. No. 359,825, filed Mar. 19, 1982 for Method and Apparatus for Continuously Producing Tandem Photovoltaic Cells. As disclosed in these applications, a substrate may be continuously advanced through successive triads of deposition chambers, wherein each chamber is dedicated to the deposition of a specific material. In making a solar cell of p-i-n type configuration, the first chamber of each triad is dedicated for depositing a p-type amorphous semiconductor material, the second chamber of each triad is dedicated for depositing an intrinsic semiconductor material, and the third chamber of each triad is dedicated for depositing an n-type amorphous semiconductor material.
The resultant roll of large area photovoltaic cells manufactured by the mass production glow discharge deposition technique described hereinabove, comprises an elongated strip of substrate upon which successive semiconductor layers are deposited. It is well known that following the deposition of the semiconductor layers, a further step must be performed in order to complete fabrication of an operable, semiconductor device. In this step, a transparent, electrically-conductive coating, which is characterized by high light-transmissivity and high electrical-conductivity, is deposited atop the semiconductor body. This elongated roll of photovoltaic material must now be processed to form therefrom a plurality of large area photovoltaic cells adapted for either series or parallel electrical interconnections.
The present invention deals with the electrical connections within and the electrical interconnections between large area photovoltaic cells. It also relates to a method of electrically interconnecting the plurality of electrically-isolated, small area segments into which the large area solar cell may be divided and provides an interconnection technique particularly adapted for assembly line production. Likewise, another concept of the present invention pertains to a method of electrically-interconnecting adjacent large area photovoltaic devices, said method also being specially adapted for assembly line production. These methods are characterized by simplicity of operation, economy of material and savings of production time as compared to the electrical connection techniques of the prior art. Note that, although a photovoltaic cell having an amorphous semiconductor body including fluorine has been described hereinabove, the present invention is not limited to amorphous semiconductors fabricated from specific process gases. Moreover, this application is equally adapted for use with photovoltaic cells of any composition, whether (1) amorphous, crystalline or polycrystalline; or (2) including fluorine. A U.S. patent application filed Sept. 23, 1982, entitled Compositionally Varied Materials And Method For Synthesizing The Materials and assigned to the same assignee as the instant patent application, provides a basis for obtaining photovoltaic quality response from materials previously tried and discarded or synthesized new materials.
U.S. patent application Ser. No. 347,779 filed Feb. 11, 1982 in the name of Prem Nath, entitled IMPROVED SOLAR CELL AND METHOD FOR PRODUCING SAME, discloses a method for subdividing a large area photovoltaic cell into a plurality of electrically-isolated, small area segments which are then electrically interconnected so as to provide an improved, high efficiency, large area photovoltaic cell. The present application, inter alia, is an improved method for economically and efficiently interconnecting these small area segments so as to form a large area photovoltaic cell, and a method for electrically interconnecting those large area cells to form adjacent electrically-interconnected large area cells. The electrically-interconnected large area photovoltaic cells so produced may be used to supply electrical power for residential or commercial consumption. Further, the electrical connections and interconnections, disclosed herein, provide for a series of pre-connected cells to be severed from an elongated strip of cells, so as to match the power requirements of a particular consumer.
The many objects and advantages of the present invention will become clear from the drawings, the detailed description of the invention and the claims which follow.